1. Field of the Invention
This invention relates to a sunlight energy conversion apparatus comprising a heat collector panel with a solar cell, and to a house air circulation system making use of the same. It also relates to a method of controlling the temperature of the photoelectric transducer.
2. Related Background Art
What is called Staebler-Wronski effect is known in the art as a phenomenon in which photoelectric transducers such as solar cells making use of non-single crystal semiconductors cause a decrease in conversion efficiency with time when exposed to light. For its control, it is known to be effective to keep the device hot or heated.
The present inventors made an experiment to obtain the results as shown in FIG. 10. FIG. 10 shows how the conversion efficiency changes with time when solar cell modules are respectively kept at 0.degree.C., 20.degree. C., 50.degree. C. and 80.degree. C. As is seen therefrom, the conversion efficiency deteriorates at a lower degree as the solar cells are kept heated at a higher temperature and also for a longer time.
Besides such data, Japanese Patent Publication No. 7-58799 discloses that photoelectric transducers can be prevented from their deterioration due to exposure to light, by enclosing the photoelectric transducers with heat insulation materials so that the service environmental temperature of the devices can be made higher than the outdoor temperature.
Japanese Patent Publication No. 7-120811 discloses that a protective film incorporated with a black pigment is provided on the back of a solar cell formed of amorphous silicon, whereby the device can be kept at a higher temperature to prevent its deterioration.
However, an attempt to rely on only a heat insulation material to maintain a higher temperature than the outdoor temperature for a long time results in a very high cost for the heat insulation material. Also, though the ground radiates heat at night, this heat can not be utilized for keeping the device hot. The present inventors examined the effect of structures kept hot using heat insulation materials and obtained the results as shown in Table 1. A device enclosed with a 50 mm thick polystyrene sheet used as a heat insulation material and another device not enclosed with a heat insulation material were tested to examine their changes in temperature in one day. As is seen from the results, the temperature rather becomes lower at dawn than the outdoor temperature even in the case of the device enclosed with a heat insulation material. This is presumed to be due to the fact that the devices can not receive the heat radiated from the ground at night. An attempt to maintain the daytime high temperature may require use of heat insulation materials in a large quantity.
Even with use of the protective film incorporated with a black pigment, the device can not be kept at well high temperature.
Meanwhile, Japanese Patent Publication No. 3-48299 discloses a "passive solar system house", where air heated by solar heat is taken from a space between a roof and a ceiling into a room through a duct and its heat is stored in a concrete slab provided underground so that the room can be efficiently warmed.
Such an air circulation system is opportune because recycled energy is utilized, but its fan used to circulate the air requires external power supply.